1. Field of the Invention
The invention generally relates to electronic connectors and, more specifically, to a capillary action enhanced surface mount pin header.
2. Description of the Prior Art
Traditionally, electrical components and particularly connectors, such as pins, have been mounted on printed circuit boards (PCBs) by extending the leads of the component or the leg portion of an upstanding pin through apertures in the board and soldered to the circuit board. The traditional approach has commonly been referred to as xe2x80x9cthrough-the-holexe2x80x9d (TTH) technology.
TTH technology has, however, been gradually replaced, for most applications, with surface mount technology (SMT), in which components as well as contacts/connectors are mounted on a surface of a PCB without forming or using apertures or holes in the circuit board. Electronic components frequently mounted in this manner include semi-conductor components, capacitors, resistors and even coils or tuned circuits. However, while SMT technology allows for rapid and efficient mounting of components on a PCB, it does present a few problems which need to be overcome in order to effectively use the technology. For one, components need to initially be accurately positioned on the lands or pads on the PCB. During such population of the board, particularly in high density configurations, the components need to be stable in their positions both before and during re-flow of solder so that the components will ultimately be fixed in desired positions or locations, as tolerances may be critical. This requires that such locations do not xe2x80x9cshiftxe2x80x9d prior to re-solder and particularly during re-solder when the components literally xe2x80x9cfloatxe2x80x9d on a layer of molten solder. This problem has been addressed, at least for individual pins, in applicant""s U.S. Ser. No. 08/600,112 for xe2x80x9cCapillary Action Promoting Surface Mount Connectorsxe2x80x9d in which a surface mount pin assembly consists of a drawn wire pin placed within an outer eyelet. The cross sectional configurations of the wire pin and eyelet form a plurality of channels spaced about the pin that promote capillary action when the eyelet is placed on a land or pad of a printed circuit board on which wire paste has been deposited and the solder re-flowed. The solder is drawn, by capillary action, up into the channels or spaces between the pin and the eyelet, removing some of the molten solder from the pad, drawing the surface mount pin assembly towards the pad or land. This provides a good electrical and mechanical connection between the surface mount pin assembly and the printed circuit board and enhances the mechanical and electrical integrity between the wire pin and the eyelet. While such surface mount pins are useful, there are numerous instances when a multiplicity of such pins must be mounted on a printed circuit board in a pin grid array. The placement of a multiplicity of such pins is both time-consuming and requires that the pins be precisely positioned on the lands, and the stability of such pins be maintained both before and after re-flow of solder. This is particularly true with high density mounting techniques which have been used in recent years in which the number of such pins or terminals per unit area has significantly increased. In some instances, header assemblies have been used to maintain the spatial relationships of a multiplicity of such pins as well as to facilitate their rapid placement on a printed circuit board.
A method of mounting surface connectors has been proposed in U.S. Pat. No. 5,303,466, where a series of pins are surface mounted on electrical pads or conductors of a printed circuit board. An insulator, which serves as a header, receives the various pins. However, the holes in the header are not plated and solder is not received within the holes by means of capillary action. The patentee proposes to initially mount the pins on the circuit board while the pins are aligned by dummy contacts and fixed to the circuit board by means of solder. It is only after the pins are mounted that the insulator is placed on the board for receiving the mating contacts in order to protect the contacts from being accidentally damaged. The insulator, therefore, does not serve any electrical function and does not serve to enhance the solder connection between the pins and the printed circuit board.
It is, according, an object of the present invention to provide a surface mount pin header which does not have the disadvantages associated with prior art headers.
It is another object of the present invention to provide a surface mount pin header which utilizes capillary action to draw the header towards the solder-coated pads or lands on a printed circuit board to prevent the header from undesired shifts of position or movements due to floating on the molten solder during re-flow.
It is still another object of the present invention to provide a surface mount pin header as in the previous objects that facilitates and speeds the attachment, by surface mounting techniques, of pin headers carrying a multiplicity of pins or other contacts.
It is yet another object of the present invention to provide a surface mount pin header that can be used to mount electrical pins and other contacts arranged in a high density array.
It is a further object of the present invention to provide a surface mount pin header of the type under consideration that can mount a great number of contacts onto a circuit board with high reliability.
It is still a further object of the present invention to provide a surface mounting method to mount high density pin arrays onto a printed circuit board while ensuring stability and positional integrity of all the pins or contacts.
It is yet a further object of the present invention to provide a surface mount pin header that exhibits a significantly higher pin retention force compared with J-lead type surface mount headers.
It is an additional object of the present invention to provide a surface mount pin header that exhibits flexibility so that a degree of board warpage is permissible and co-planarity problems are minimized.
It is still an additional object of the present invention to provide a surface mount pin header that provides a visual indicator that proper mounting has been effected, thereby providing higher quality assurance of production.
It is yet an additional object of the present invention to provide a surface mount pin header as in the previous objects that exhibits high resistance to thermal shock and thermal cycling.
In order to achieve the above objects, as well as others which will become apparent hereinafter, a surface mount pin header in accordance with the present invention, which promotes capillary action, comprises a first substantially flat substrate provided with a predetermined array of plated-through holes having substantially parallel axes and each having an internal surface defining a first substantially uniform cross section. A plurality of pins are provided each defining a longitudinal axis and having one end extending through an associated plated-through hole and another end extending from one side of said first substrate. Each said pin has an external surface on at least said one end or portion thereof received within an associated plated-through hole that defines a second substantially uniform cross section. Said first and second cross sections are dissimilar and configured to provide spaced lines of contact and elongate channels substantially parallel to said axes, between said internal and external surfaces and between adjacent lines of contact. Said channels are dimensioned to promote capillary action for molten solder at a channel opening on one side of said first substrate to cause the solder to be drawn through said channel towards the opposite side of said first substrate. A second substantially flat substrate is provided for positioning solder at points substantially aligned with points on said predetermined array and proximate to at least one channel in at least one plated-through hole prior to melting of the solder. In this manner, melting of the solder causes the solder to flow into said at least one channel in said at least one plated-through hole and to urge said second substrate to be drawn towards said first substrate to provide a reliable solder joint with said pin and said plated-through hole. In the presently preferred embodiments said second substrate provides solder aligned with all said channels of all said plated-through holes in said predetermined array.